Irena Sendler, who has died in a Warsaw hospital at the age of 98, was one of the heroes of the Nazi occupation of Poland. As a member of Zegota, the Council for Providing Aid to the Jews, an organisation set up by the Polish underground state and financed by the Polish government-in-exile in London, she succeeded in saving around 2,500 Jewish children in the Warsaw ghetto from certain death in the Nazi extermination camps.

Born in Otwock, a resort town near Warsaw much frequented by Jews before the war, Sendler was the only daughter of a doctor, Stanislaw Krzyzanowski, known for his sympathetic approach towards his Jewish neighbours. Unusually for a Catholic child, Sendler was allowed to play with Jewish children as she grew up. She studied Polish literature and became active in the Polish Socialist party. At the time of the Nazi invasion of Poland in 1939, she was also working as a social care nurse for the Warsaw city welfare department.

During the Nazi occupation, conditions for the Jews in Warsaw deteriorated dramatically as more than 400,000 people were confined in the city's ghetto, an area of perhaps four square kilometres, which was then, in 1940, sealed off. Sendler was involved in providing assistance to those in need, and in December 1942 - soon after the deportation of Jews had begun to the Treblinka death camp - she became head of the children's department of Zegota. She was motivated, above all, by her sense of social justice and her feelings of obligation to her Jewish friends.

When the German authorities decided finally to liquidate the Warsaw ghetto in 1943, Sendler was one of a group of around 20 Zegota members who organised the evacuation of children, placing them in Polish families, orphanages and convents. She was able to move around the ghetto legally, disguised as a public-health nurse responsible for investigating a suspected typhus epidemic. Sometimes, the children were hidden in a lorry driven by a fellow conspirator, Antoni Dzbrowski. A mechanic reportedly hid babies in his toolbox. At other times, they were given sleeping draughts and transported to what was known as the "Aryan" side - outside the ghetto - in baskets, or chests in ambulances or streetcars. German officials were told they had died of typhus.

The escaping children were provided with false identities, and many of those who remained in Poland were taught Christian prayers so they would blend into the community more easily. But their real names and details of their families were written down in code and buried in jam jars, which were dug up after the war. This meant that once the conflict was over the children were able to discover who they really were.

In October 1943, at the height of this rescue operation, Sendler was arrested by the Gestapo. She was brutally tortured in the notorious Pawiak prison and sentenced to death. But she never revealed details of her contacts and, by bribing her guards, other members of Zegota were able to obtain her release.

After Poland's liberation in 1945, Sendler returned to the Warsaw social welfare department, co-founding an orphanage and an old people's home and organising a service to deal with women and children in need. She stayed in contact with some of the children she had rescued, many of whom eventually found their way to Palestine.

There was little recognition for Sendler's work in Poland in the immediate aftermath of the war, but in 1965 she was awarded the title of "Righteous Among the Nations" by the Yad Vashem Holocaust memorial centre in Jerusalem, and in 1991 was granted honorary citizenship by the state of Israel. In 2006 she was nominated for the Nobel peace prize by an American teacher, Norman Conrad, whose students had written a play and made a documentary film about her, entitled Life in a Jar. By now her candidacy was supported by the Polish president, Lech Kaczynski, and the prime minister of Israel, Ehud Olmert. Her Polish awards included the Jan Karski award for moral courage (named after a Polish resistance fighter), the Order of the White Eagle and honorary citizenship of Warsaw. In 2006, a biography of her appeared in Germany and Poland.

Last year, her work was recognised by the Polish senate, which unanimously passed a resolution praising her work in rescuing "the most defenceless victims of the Nazi ideology - the Jewish children". Ill-health prevented her from attending the ceremony, but in a letter to the senate she wrote: "Every child saved with my help and the help of all the wonderful messengers who are today no longer alive is the justification for my existence on this earth, rather than a claim for honour."

The greatness of Sendler's achievements was widely accepted. According to Elzbieta Ficowska, one of those saved as a five-month-old baby in July 1942 and now the wife of a leading Polish poet: "It took a miracle to save a Jewish child. Sendler saved not only us, but also our children and grandchildren and the generations to come'.

According to Shevach Weiss, the former Israeli ambassador to Poland, who himself survived with a Polish family during the Nazi occupation: "Irena Sendler should be seen as the Righteous among the Righteous. Poles and Jews have a trio of heroes in common; Pope John Paul II, Janusz Korzak and Irena Sendler."

Ill-health prevented Sendler from receiving the presidents of Poland and Israel on the occasion of the 65th anniversary of the Warsaw ghetto rising last month. Sadly, too, she died on the same day as a ceremony naming a Warsaw school, Gymnasium No 23, in her honour.

Her first marriage was to Mieczyslaw Sendler; they divorced shortly after the war. She then married a fellow member of the underground, Stefan Zgrzembski, with whom she had two sons and a daughter. One son died a few days after his birth and the second, Adam, died of heart failure in 1999. She is survived by her daughter and a granddaughter.

· Irena Sendler, social worker and rescuer of Warsaw Jews, born February 15 1910; died May 12 2008

· This article was amended on Tuesday May 20 2008. The Warsaw ghetto was something over four square kilometres in size, rather than one square kilometre as we said in the obituary of Irena Sendler. This has been corrected.